1. Field of the Invention
This invention relates to crosslinking agents and curable compositions containing the same. In particular, the present invention is directed to substituted urea and oxime carbamate modified amino crosslinking agents of triazines or glycolurils. The invention also relates to a novel process for preparing pyrrolidone urea. The invention further relates to curable compositions containing the novel crosslinkers of the invention, including curable powder coating compositions.
2. Related Prior Art
Curable compositions containing amino crosslinking agents have long been known. For example, U.S. Pat. No. 3,661,819 discloses aminotriazine crosslinking agents comprising a triamino compound represented by the formula ##STR1## or a benzoquanamine compound represented by the formula ##STR2## wherein R is hydrogen or alkyl of from 1 to 12 carbon atoms. It is also known to use oligomers of such compounds, which are low molecular weight condensation products containing two, three or four triazine rings, joined, for example, by --CH.sub.2 OCH.sub.2 -- and/or --CH.sub.2 -- linkages, as well as mixtures thereof.
These aminotriazine crosslinking agents have been used to self-condense or cure active hydrogen-containing materials, such as polymers containing carboxyl groups, alcoholic hydroxy groups and amide groups. When such curable compositions are applied to substrates as coatings or used as binders for glass fibers or for foundry sand, and then cured, excellent properties in terms of hardness, solvent resistance, tensile strength and so forth are imparted to the article.
Other triazine compounds having excellent properties are also known. For example, U.S. Pat. Nos. 4,708,984 and 4,710,542 disclose amino triazine compounds and oligomers thereof having, respectively, beta-hydroxyalkylcarboxyl methyl and alkylcarbamylmethyl functionality. In addition, aminotriazine crosslinkers having tricarbamoyl functionality are disclosed in U.S. Pat. No. 5,084,541.
U.S. Pat. No. 4,133,843 discloses a process for preparing a curable powder resin which includes the step of condensing a methylol urea or methylolaminotriazine with an aliphatic alcohol having one, two, three or four carbon atoms and a reactive compound containing a hydroxyl or amide. The reactive compounds generally include aliphatic diols and polyols, aliphatic diamides and polyamides, aromatic alcohols, aromatic sulfonamides and phenols. Ureas and carbamates are not disclosed.
A water dispersible coating composition containing an acrylic polymer having active hydrogen functionality and quaternary ammonium salt functionality along with a blocked polyisocyanate is disclosed in U.S. Pat. No. 4,444,954. This patent discloses a multitude of organic polyisocyanate compounds, including triisocyanates, and blocking agents, such as urea and oxime types, which are said to be useful for forming a blocked polyisocyanate. There is no disclosure, or suggestion in this or any of the other patents cited herein of an amino crosslinking agent having substituted urea or oxime blocked carbamate functionality.